The NFL's collective bargaining agreement, which governs such disputes, makes clear that the failure to sign a player is not in itself enough to prove collusion. Instead, it must be combined with evidence that teams entered into an agreement, express or implied, to bar the player's employment.

Here's the relevant wording of the CBA's "burden of proof" for collusion:

"The failure by a club or clubs to negotiate, to submit offer sheets, or to sign contracts with restricted free agents or transition players, or to negotiate, make offers, or sign contracts for the playing services of such players or unrestricted free agents, shall not, by itself or in combination only with evidence about the playing skills of the player(s) not receiving any such offer or contract, satisfy the burden of proof set forth …"

Kaepernick began sitting or kneeling during the national anthem while with the San Francisco 49ers in August 2016, protesting what he said was police brutality and racism. He has remained unemployed since opting out of his contract in March. The Seattle Seahawks worked him out in May, and the Baltimore Ravens considered signing him this summer, but there have been no reported contract offers.

But his grievance, filed by attorney Mark Geragos, does not provide any specific evidence of an agreement to collude. It vaguely references NFL general managers who have cited "directives from NFL owners to not let Kaepernick so much as practice with an NFL team." It also accuses owners of submitting to the demands of President Donald Trump, whom it terms "an organizing force" in squashing what has become a weekly protest among at least some NFL players.

In the end, however, Geragos asserts that "the mere suspicion of collusion against Mr. Kaepernick has risen to the level of concrete and actual collusion. It is no longer a statistical anomaly but instead a statistical impossibility that Mr. Kaepernick has not been employed or permitted to try out for any NFL team since the initiation of his free agency period."

It'd be hard to seriously argue that Colin Kaepernick couldn't help certain NFL teams on the field this season. Ezra Shaw/Getty Images

Reasonable people can debate Kaepernick's skill and ability level. But it would be impossible to rank him below the 89 quarterbacks on NFL rosters as of last Friday. There is no question that he is a better quarterback than some who have jobs, and perhaps some who have starting jobs as well.

But that fact -- and yes, I'm comfortable calling it a fact -- doesn't seem to satisfy the burden of proof required by the CBA. It seems clear that all 32 teams have reached the same conclusion on Kaepernick, if for different reasons. If that's the result of a coordinated league effort, however, we haven't seen the evidence required for an arbitrator to agree.

To be clear, none of this is going to accelerate Kaepernick's return to the NFL. Even if he wins this grievance, the CBA doesn't require a team to give him a job. Instead, it spells out a process for awarding compensatory damages, at a value to be determined by the arbitrator. The real damage to the NFL could be an exposure of its inner workings via public discovery.

There will be more to come from this story, for sure. NFL owners will gather this week, in fact, to discuss how to address the player protests in a way that alleviates public scrutiny while also providing players a fair working environment. Kaepernick's filing will add a new level of intensity to those proceedings, but its path to success is unclear at best.